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Researchers split over importance of latest stem cell discovery

Scientists in the US have used genetically modified stem cells to repair heart damage in rats following a heart attack, but it is unclear whether the breakthrough will ultimately benefit human patients.

In previous experiments using stem cells to try and treat heart damage, virtually all stem cells died within four days of being injected. However, Victor Dzau and his team from Harvard Medical School inserted a gene called Akt1 into stem cells derived from bone marrow, and found that the gene blocked the signal that triggers cell suicide.

Using rat models, the modified cells halted the heart's subsequent decline towards failure, and within two weeks the rats' hearts were back to normal health. The team believes that the modification allowed the cells to survive long enough to become heart muscle cells, replacing the damaged tissue.

The result strengthens the theory that stem cells could be used to mend human hearts after attacks, and its supporters also point to positive findings following clinical trials where heart attack patients are injected with their own stem cells.

However, other experts question whether such stem cell treatments will prove to be effective or even safe in humans. Charles Murray, from Washington State University, argues that some human studies have lacked the appropriate control groups. 'One needs to be enthusiastic but sceptical,' he says.

It is also unclear exactly how stem cells are healing the rats' hearts. Possible explanations suggest that they may transform into new muscle cells, fuse with existing cells, or simply cause existing cells to repair and grow themselves.

Despite the questions still surrounding the use of stem cells in humans, however, supporters argue that preliminary human trials must be allowed to continue due to the pressing need for heart therapies. Around 23 million people worldwide are thought to be affected by heart failure.